It is well known that patients in neurological clinics with seemingly similar lesions do not always display the same deficits or signs of pathology. While this has been attributed to "individual differences," such terms are only descriptive and really convey no information about why this should be the case. The present program is concerned with differences in behavior following seemingly similar brain lesions and attempts to delineate some of the factors that can affect post-traumatic performance. Among the independent variables that will be assessed are the significance of training and "overtraining" prior to brain damage, the duration of the postsurgical recovery period, and whether the lesions are inflicted all at once or in a number of stages ("serial lesions"). Studies also are planned to examine the effects of complex environments, drug administration, and age on recovery of function. In many of our investigations we will be using high-speed cinematography and the somatosensory forebrain (somatic cortex and ventrobasal complex) as a model system. These experiments will concentrate on tactile discriminative behavior in the rat. In some cases, however, we plan to look at other CNS structures in the context of somesthetic responsivity. For example, we hope to study the conditions under which rats will swim and save themselves after lesions of the posterior hypothalamus, and whether preoperative insulin injections can attenuate deficits on avoidance problems after caudate nucleus lesions. We also hope to examine whether mice with brain damage live as long as those that have intact nervous systems, and whether they die of the same diseases. This basic problem has not been studied in the past, although it could have important implications for professionals contemplating biopsies and other intrusive techniques. It is felt that "individual differences" in response to brain damage will become more comprehensible as a result of this program. Furthermore, we believe that more accurate prognoses and effective therapies will be possible once the effects of variables such as those mentioned above can be understood. Finally, some long-range effects of brain damage (e.g., longevity, susceptibility to disease) should be clarified as a result of this program.